Nitric oxide is an important inter and intra-cellular messenger which has been implicated in the pathogenesis of septic shock. Inhibition of nitric oxide synthase is under investigation as a treatment for hypotension in septic shock. In addition to the vasodilating effect of nitric oxide on vascular smooth muscle, nitric oxide also has effects on platelets and immune cells. In this investigation, we are examining the role of the nitric oxide pathway as a modulator of immune cell function. We have found that nitric oxide regulates cytokine production by human phagocytic cells. (J Immunol, 1994). Further, nitric oxide regulates IL-8 release from human neutrophils, but neither nitric oxide or nitric oxide synthase inhibitors appear to directly alter neutrophil chemotaxis (manuscript in preparation, 1995). Recent work has focused on determining whether human immune cells actually produce nitric oxide and if so under what conditions, and on defining nitric oxide dependent interactions between the endothelium and phagocytic cells. Data from this project suggest that human neutrophils do not make nitric oxide under a variety of conditions (J Immunol, 1994). However, nitric oxide may play an important role in the interaction between neutrophils and other cells including macrophages, endothelium and bronchial epithelial cells. Currently, we have made vectors to transfect nitric oxide synthase into human phagocytic cell lines. Using these vectors we have successfully transfected U937 cells (a human monocytic cell line) with human endothelial cell nitric oxide synthase and with mouse, inducible nitric oxide synthase. We will examine the effect of nitric oxide production in these cells on function (chemotaxis, superoxide production, cytokine release, cell-surface marker expression) and resistance to infection.